RESUMO
We investigated the impact of respiratory syncytial virus (RSV) infection, an important asthma precipitant, on endothelin receptor function and release in sheep bronchial explants. RSV infection was confirmed using polymerase chain reaction and immunohistochemistry. Since sheep airway smooth muscle contains only endothelin-A receptors, sarafotoxin (Stx) S6c did not cause airway contraction. In contrast, sarafotoxin S6c (300 nM) caused contraction in RSV-infected bronchial explants (8 +/- 3% carbachol Emax). However, we could not detect airway smooth muscle endothelin-B receptors in explants using autoradiography. RSV infection per se did not alter the release of immunoreactive endothelin from sheep bronchial explants (control = 11.6 +/- 0.9 pg versus RSV = 12.1 +/- 0.9 pg). Interestingly, dexamethasone (1 microM) alone increased endothelin release in both control (17.9 +/- 2.0 pg) and RSV-infected tissue (18.3 +/- 3.1 pg). The combined presence of protease-activated receptor-2 (PAR-2) ligand (100 microM) and dexamethasone (1 microM) also increased endothelin release from control tissue (17.3 +/- 1.4 pg), but endothelin release was suppressed by PAR-2 ligand in RSV-infected tissue (10.3 +/- 0.8 pg), probably because PAR-2 expression was increased by RSV. In summary, the novel expression of endothelin-B receptors triggered by RSV might be relevant to RSV-associated asthma. Furthermore, activation of airway PAR-2 may be protective in asthma where endothelin levels are elevated in part via endothelin release suppression.
Assuntos
Brônquios/metabolismo , Contração Muscular , Músculo Liso/metabolismo , Receptor de Endotelina B/metabolismo , Infecções por Vírus Respiratório Sincicial/metabolismo , Animais , Brônquios/efeitos dos fármacos , Brônquios/fisiopatologia , Brônquios/virologia , Meios de Cultivo Condicionados/metabolismo , Dexametasona/metabolismo , Dinoprostona/metabolismo , Relação Dose-Resposta a Droga , Endotelina-1/metabolismo , Ensaio de Imunoadsorção Enzimática , Feminino , Indometacina/farmacologia , Masculino , Contração Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Músculo Liso/fisiopatologia , Músculo Liso/virologia , Oligopeptídeos/farmacologia , Peptídeos Cíclicos/farmacologia , Piperidinas/farmacologia , Receptor de Endotelina A/metabolismo , Receptor de Endotelina B/efeitos dos fármacos , Receptor PAR-2/metabolismo , Infecções por Vírus Respiratório Sincicial/fisiopatologia , Ovinos , Fatores de Tempo , Técnicas de Cultura de Tecidos , Venenos de Víboras/farmacologiaRESUMO
Within the airways, endothelin-1 (ET-1) can exert a range of prominent effects, including airway smooth muscle contraction, bronchial obstruction, airway wall edema, and airway remodeling. ET-1 also possesses proinflammatory properties and contributes to the late-phase response in allergic airways. However, there is no direct evidence for the contribution of endogenous ET-1 to airway hyperresponsiveness in allergic airways. Allergic inflammation induced in mice by sensitization and challenge with the house dust mite allergen Der P1 was associated with elevated levels of ET-1 within the lung, increased numbers of eosinophils within bronchoalveolar lavage fluid and tissue sections, and development of airway hyperresponsiveness to methacholine (P < 0.05, n = 6 mice per group). Treatment of allergic mice with an endothelin receptor antagonist, SB-217242 (30 mg x kg(-1) x day(-1)), during allergen challenge markedly inhibited airway eosinophilia (bronchoalveolar lavage fluid and tissue) and development of airway hyperresponsiveness. These findings provide direct evidence for a mediator role for ET-1 in development of airway hyperresponsiveness and airway eosinophilia in Der P1-sensitized mice after antigen challenge.